Piezoelectric ceramic composition



Sept. 22, 1970 su o AKAsHl ETAL 3,530,012

PIEZOELECTRIC CERAMIC COMPOSITION Original Filed Oct. 17. 1966 4 Sheen s-Sheet 1 f fi\\ I200 I I 1 I 00 I 0 I MECHA lwc4L QUALITY FACTOR 4 5: TPOMECHAN/Ci COUPLING #46700 P (PERCEN mass) 0 002 an; am 0.20, aso 0.5

l N VEN'TORS 7S UNEO AKASH/ M4540 MKAIMSHI TOME-ll OHNO A 7 ran: v5

Sept. 22, 1970 su o AKASHI ETAL 3,530,072

PIEZOELEQTRIC CERAMIC COMPOSITION Original Filed Oct. 17. 1966 r 4 Sheets-Sheet 2 I V I -w 1 a I I (I I, 0 1 H r .4 .4 a 0 0 0 0 W W 6 M 9. \MM wk EWUQMnQ 6', 0 mum 610,0 F l G. 2

Sept. 22, 1970 TSUNEO AKAsHl ETAL 3,530,072

PIEZQELECTRIC CERAMIC COMPOSITION Original Filed Oct. 17, 1966 4 Sheets-Sheet 4 FIGA United States Patent 3,530,072 PIEZOELECTRIC CERAMIC COMPOSITION Tsuneo Akashi, Masao Takahashi, and Tomeji Ohno,

Tokyo, Japan, assignors to Nippon Electric Company,

Limited, Tokyo, Japan, a Japanese corporation Original application Oct. 17, 1966, Ser. No. 587,242, now

Patent No. 3,481,875. Divided and this application Apr. 15, 1969, Ser. No. 817,274

Claims priority, application Japan, Nov. 10, 1965,

40/69,028; Dec. 24, 1965, 40/751,737 Int. Cl. C04b 35/00 US. Cl. 252-62.9 3 Claims ABSTRACT OF THE DISCLOSURE A piezoelectric ceramic composition of the formula (Pb A (Zr Ti Sn )O Where A represents at least one member selected from a group consisting of calcium, strontium and barium and u, v, x, y and z are given by and x+y+z=l.00, characterized in that said ceramic composition contains a set of additional constituents consisting of a chromium compound equivalent in amount to a chromium sesquioxide of from 0.01 to 0.30 weight percent and a cobalt compound equivalent in amount to a cobalt sesquioxide of from 0.02 to 0.50 weight percent, each of the weight percentages being the percentage of the total weight of said ceramic composition.

This is a division of application Ser. No. 587,242 filed Oct. 17, 1966, now U.S. Pat. No. 3,481,875.

This invention relates generally to piezoelectric ceramic compositions. More particularly, the invention relates to ceramic compositions based on a formula of lead zirconate-lead titanate PbZrO =PbTiO or on a formula lead zirconate-lead titanate-lead stannate The present invention relates more particularly to lead zirconate-lead titanate-lead stannate ceramic compositions which contain, in addition to such compositions, chromium sesquioxide (Cr O of from 0.01 weight percent to 0.3 weight percent of the total weight and also cobalt sesquioxide (C0 0 of from 0.02 Weight percent to 0.5 weight percent.

More particularly, the present invention also relates to PbZrO =PbTiO =PbSnO ceramic compositions which contain, in addition to such compositions, manganous oxide (MnO) of from 0.02 weight percent to 0.5 weight percent of the total weight and also cobalt sesquioxide (C0 0 of from 0.02 weight percent to 0.5 weight percent.

A general object of this inevntion is to proivde ceramic compositions having large electromechanical coupling factors and large mechanical quality factors.

A further object of this invention is to provide piezoelectric materials which have both large electromechaniice cal coupling factors and large mechanical quality factors for use as elements of ceramic electric Wave filters and as transducer elements of mechanical filters.

It can be established that a lead. zirconate-lead titanate solid solution Pb(ZrTi)O obtained by sintering a mixture of lead zirconate PbZrO and lead titanate P=bTiO has piezoelectric properties which are stable against change of temperature and elapse of time and that strong piezoelectric activities are achieved in the neighborhood of x=0.52-0.54 in Pb(Zr :Ti O

Fundamental measures for evaluating the piezoelectric properties of a piezoelectric material are its electromechanical coupling factor and its mechanical quality factor. The electrochemical coupling factor represents the efiiciency of transforming electric oscillation into mechanical vibration and, conversely, of tarnsforming mechanical vibration into electric oscillation. The mechanical quality factor represents the reciprocal proportion of the energy consumed by the material during the electrical and mechanical energy interconversion. A larger mechanical quality PfQCtOI corresponds to a smaller energy consumption by the material, and vice versa.

Recently, attention and studies have been directed to ceramic electric wave filters wherein use is made of piezoelectric ceramics as the element or elements of the filters, and to mechanical filters wherein use is also made of piezoelectric ceramics as the transducer or tranducers thereof. The qualities desired for the piezoelectric ceramics used in these fields of applications are as follows: For the elements of ceramic electric wave filters, the electromechanical coupling factor must have a desired value selected from a range between an extremely large value and a very small value, and the mechanical quality factor should have as great a value as possible. For the transducer elements of mechanical filters, both the electromechanical coupling factor and the mechanical quality factor must be as large as possible. Thus, the properties required for the transducer elements of mechanical filters are consistent with that particular set of properties demanded for the elements of ceramic electric wave filters in which the electromechanical coupling factor is large.

The electrochemical coupling factor determines the frequency spacing between the attenuation poles of the filter in such a manner that a greater electromechanical coupling factor produces a filter of wider frequency spacing and a smaller electromechanical coupling factor results in a filter of narrower frequency spacing. In other words, the electromechanical coupling factor of the piezoelectric material for the elements of ceramic filter must be selected in compliance with the frequency spacing between the attenuation poles of the particular filter in which the material is to be used and that factor must therefore be available or adjustable between an extremely small value and a very large value according to the characteristics of the filter. The mechanical quality factor also determines the loss in the pass band and the loss at the attenuation poles of the filter. The values desired for a filter therefore determine the lowest allowable limit of the mechanical quality factor of the piezoelectric material to be used in the filter. In other words, a piezoelectric material having a smaller mechanical qaulity fac tor than required can not provide a satisfactory filter,

zirconate-lead titanate ceramics.

while a piezoelectric material having a greater mechanical quality factor than required can easily provide a filter of excellent characteristics. A greater mechanical quality factor is generally necessary for piezoelectric materials to be used in a filter of narrower pass band or for a case where a smaller electromechanical coupling factor is required.

As has so far been described, piezoelectric material for use in filters must be furnished with the electromechanical coupling factor selected from a wide range according to the characteristics and the fields of application of the particular filter and with the largest possible mechanical quality factor.

According to this invention, the basic composition of lead zirconate-lead titanate Pb (Zr Ti )O may incorporate either one of two pairs of additives above-noted, that is, Cr O and C 0 or MnO and C0 0 in the required amounts, and in such basic composition at least one member of the group of barium (Ba), strontium (Sr) and calcium (Ca) may replace up to 25 atom percent of the lead (Pb) contained in the basic composition.

Details of certain earlier types of replacements or substitutions in piezoelectric materials are generally described, for example, in Journal of the National Bureau of Standards, 55 (1955), 239 by B. Jaife, R. S. Roth, and S. Marzullo and in US. Pats. No. 2,906,710 issued to F. Kulcsar et al. on Sept. 29, 1959, and No. 3,068,177 issued to J. A. Sugden on Dec. 11, 1962.

This invention may also be expressed as residing in a piezoelectric ceramic composition whose basic composition may be a lead zirconate-lead titanate-lead stannate PbZrO -PbTiO -PbSnO solid solution as already noted. This basic composition may be expressed by the term Pb (Zr Ti Sn 0 where the ranges for x, y, and z are mol ratios given by x=0.000.90, y=0.100.60, z=0.00-0.65, and x+y+z =l.00,

in order that the piezoelectric material may have an electromechanical coupling factor of a satisfactory value Compositions outside of the suggested ranges are not practically operable because of their seriously reduced electromechanical coupling factors. The largest electromechanical coupling factor is obtainable in cases in which x, y, and z are in the vicinities of 0.52-0.53, 0.48-

0.47, and 0.00, respectively. Also, excellent piezoelectric properties are obtained even if at least one member of the group of calcium, strontium and barium may be substituted for up to 25 atom percent of the lead contained in the basic composition.

It is especially noted, as will be explained by way of example, that improvements in the characteristics of the various compositions may be brought about by the addition of cobalt sesquioxide, chromium sesquioxide and manganous oxide in the amounts and in the combinations specified hereinafter, and such improvements clearly result from the presence of cobalt ions, chromium ions and manganous or manganese ions, respectively, in the lead Similar cobalt compounds (for example, CoCO other than cobalt sequioxide (C0 0 may also be used in the composition so as to provide an amount of cobalt ions equal to the amount of cobalt ions provided by cobalt sesquioxide (C0 0 when it is used in the composition. Also, similar chromium compounds (for example, CrCl other than chromium sesquioxide (Cr O may be used in the com position so as to provide an amount of chromium ions equal to the amount of chromium ions provided by chromium sesquioxide (Cr 0 when it is used in the composition. Furthermore, if manganous or manganese compounds, other than MnO, are utilized, they should be used in amounts equivalent to the desired weight of MnO.

Particularizing further, the compositions of this invention may also consist of another basic composition of Pb(Zr Ti Sn )O where x, y, and z are given by the above equations and where at least one member of the group of calcium, strontium and barium may be replaced by up to 25 atom percent of lead (Pb) contained in the basic composition, and such basic composition may include additional constituents of cobalt sesquioxide (Co CO of from 0.02 weight percent to 0.5 weight percent and also manganese oxide (MnO) of from 0.02 weight percent to 0.5 Weight percent.

The resulting basic compositions above-noted are especially suitable as piezoelectric materials for the elements of electric wave filters and for the transducer elements of mechanical filters.

As for the piezoelectric materials to be used in the elements of ceramic electric Wave fiters, it is necessary that such materials provide an electromechanical coupling factor with an optimum value selected from a wide range extending from an extremely large value to a very small value, and it is also desirable for the mechanical quality factor to have as great a value as possible. This criterion is described, for example, in Electronic Engineering, vol. 33 (1961), No. 3, pp. 171-177, by R. C. V. Macario, entitled, Design Data for Band-Pass Ladder Filters Employing Ceramic Resonators.

This invention will be better understood from the more detailed description hereinafter following when read in connection with the accompanying drawing in which:

FIG. 1 shows curves representing the electromechanical coupling factor Kr for the radial mode vibration and the mechanical quality factor Qm, both plotted as ordinates, against abscissae representing the content of cobalt sesquioxide (C0 0 in ceramics obtained by adding, to the composition Pb (Zr Ti )O the compound chromium sesquioxide (Cr O of 0.1 weight percent and the compound cobalt sesquioxide (C0 0 of up to 0.5 weight percent. This composition is exemplified in Table 1 hereinafter.

FIG. 2 shows curves representing the factors Kr and Qm, both plotted as ordinates, against abscissae representing the content of chromium sesquioxide (Cr O in ceramics obtained by adding, to the composition the compound cobalt sesquioxide (C0 0 of 0.10 weight percent and the compound chromium sesquioxide (Cr O of up to 0.3 weight percent. This composition is exemplified in Table 2 hereinafter.

FIGS. 3 and 4 show similar curves representing the electromechanical coupling factor Kr for the radial mode vibration and the mechanical quality factor Qm. The abscissae of FIG. 3 are related to the compound C0 0 while the abscissae of FIG. 4 are related to the compound MnO. The curves of FIG. 3 are based on the compositions given in Table 6 while the curves of FIG. 4 are based on the compositions given in Table 7.

EXAMPLE 1 Results shown in Table 1 So that the resulting basic composition may be represented by Pb(Zr Ti )O namely, by x=0.52 and y=0.48, a powder consisting of 50 mol percent of lead monoxide (PbO), 26 mol percent of zirconium dioxide (ZrO and 24 mol percent of titanium dioxide (TiO' a compound of 0.10 weight percent of chromium sesquioxide (Cr O as an additional constituent, and another compound of cobalt sesquioxide (C0 0 as a further additional constituent, arranged in various proportions between 0.02 weight percent and 0.50 weight percent as indicated in Table 1, are mixed, respectively, in a ball mill. Mixed powder of the respective kinds is presintered at 900 C. for an hour, crushed, press-moulded into discs, and sintered at 1300 C. for an hour. The resulting ceramic discs are provided with silver electrodes and piezoelectrically activated through polarization treatment at 100 C. for an hour under an electric field of 50 kv./cm. After the discs have been allowed to stand for 24 hours, the electromechanical coupling factor Kr for the radial mode and the mechanical quality factor Qm are measured 6 EXAMPLE 2 Results shown in Table 2 The results are shown in Table 2, which are obtained for a mixture of the same basic composition as that to evaluate the piezoelectric activities. Typical results are 5 involved in Example 1, with an additional constituent of shown in Table 1.

cobalt sesquioxide (C 0 of 0.10 weight percent, and

TABLE 1 No. Composition percent Qm Pb (ZIo,52Tiu,4s)O 42 250 2.- Pb (ZI'o 52Tlo,4g)O3 plus 0.10 wt. percent GU03 52 780 3.- Pb (Zro,5zTio,4s)O plus 0.10 wt. percent OM0 plus 0.02 wt. percent C0203... 56 1,070 4.. Pb (ZIo 52Tl0 4s)03 plus 0.10 wt. percent ClzOa plus 0.05 wt. percent C0205 60 1,240 5. Pb (Zro.5zTi0 4)O3 plus 0.10 wt. percent CrzOa plus 0.10 wt. percent CozOa. 61 1, 290 6. Pb (Zl0 52Tio,4s)Oa plus 0.10 wt. percent Orzo; plus 0.20 wt. percent 0010; 60 930 7 Pb (Zr 52Tio is)Oa plus 0.10 wt. percent ClzOs plus 0.30 Wt. percent C0203 60 840 8 Pb (Zl'uszTiuAQOs plus 0.10 wt. percent CrzOs plus 0.50 wt. percent (30203--.. 800

l Cobalt carbonate 0000s is added as calculated on the basis of 00203.

Comparison between the results Nos. 1 and 2 of Table 1 shows that the addition of 0.10 weight percent of Cr 0 alone to the basic composition provides a piezoelectric with further additions of chromium sesquioxide (Cr O of from 0.01 weight percent to 0.30 weight percent as shown in Table 2.

TABLE 2 Kr, No Composition percent Qm Pb (Zru 2'1io ia) 03 plus 0.10 wt. percent C0103 56 350 10. Pb (Zlo.52Tlu.4s)0a plus 0.01 wt. percent CrzOs plus 0.10 wt. percent 0020 58 440 11. Pb (ZIO.52Ti0,4g)O3 plus 0.02 wt. percent Cl'zOa plus 0.10 wt. percent C0.-2Oa----. 60 900 12. Pb (Zru.62Tlo,t5)O3 plus 0.05 wt. percent ClzOs plus 0.10 wt. percent 00201..." 64 1, 270 13... Pb (Zro.szTiu.4s)Os plus 0.20 wt. percent OM03 plus 0.10 wt. percent 00203"... 57 90 14 Pb (Zro.5zT1o.4s) 03 plus 0.30 wt. percent CrzOs plus 0.10 wt. percent 0020s.- 56 780 1 01'2 (SO03 was added as calculated on the basis of CrzOa.

material having substantially raised Kr and Qm factors. Further increases in the Kr and Qm factors, which have already been increased by the addition of Cr O provide still greater improvements in the piezoelectric materials which would have wider fields of application. Comparison of the results Nos. 1 and 2 with the results Nos. 3 through 8 proves that addition or both Cr O and from 0.02 weight percent to 0.50 weight percent of C0 0 greatly increases the Kr and Qm factors. In general, an increase in one of the Kr and Qm factors results in a decrease in the other factor. However, the addition of both Cr O and C0 0 to the basic composition improves both the Kr and Qm factors and makes is possible to realize piezoelectric materials having Kr and Qm factors both of which are increased in magnitude. This material is excellent for use as the piezoelectric material in ceramic electric wave filters where a large Kr factor is required and in transducers of mechanical filters.

Referring to FIG. 1, the above-mentioned relation between the content of C0 0 and the piezoelectric prop- .erties Kr and Qm are plotted for results Nos. 2 through 8 of Table 1. The curves quite clearly show that excellent piezoelectric materials are produced when the content of C0 0 falls between 0.02 Weight percent and 0.50 weight percent.

If the content of C0 0 is less than 0.02 weight percent, the combination or coexistence of Cr O and C0 0 hardly improves the piezoelectric activities achieved by the presence of Cr O alone. If the content of C0 0 exceeds 0.50 weight percent, no substantial improvement is obtained in the factors Kr and Qm which would otherwise be attained through the coexistence of Cr O and C0 0 More particularly, if Cr O is added when the proportion of C0 0 is greater than 0.50 weight percent, the presence of C0 0 alters the piezoelectric properties as already noted and the addition of Cr O hardly contributes to the improvement of the properties.

In view of the above, a range between 0.02 weight percent and 0.50 weight percent is selected for the elfective content of C0 0 Comparison of the result No. 9 with the result No. 1 of Example 1 shows that addition of 0.10 weight percent of C0 0 alone to the basic composition provides a piezoelectric material having considerably elevated Kr and Qm factors. It should be understood, however, that further increases in the Kr and Qm factors, otherwise raised by addition of C0 0 would provide piezoelectric materials of considerable improvement and having wider fields of application. Such further increases are achieved as shown in Table 2, by addition of both Cr O and C0203.

Referring to FIG. 2, the piezoelectric properties Kr and Qm are plotted versus the content of Cr O with respect to the results cited in Table 2 and to the result No. 5 of Table 1. The curves quite clearly show that excellent piezoelectric materials are obtainable when the content of Cr O falls between 0.01 weight percent and 0.30 weight percent.

Even with coexistence of Cr O as additives to the basic composition above-noted, less than 0.01 weight percent of Cr O hardly improves the piezoelectric properties otherwise attained by the addition of C0 0 alone. Also, when more than 0.30 weight percent Cr O is added, improvement in the properties by coexistence of Cr O and C0 0 is hardly expected.

In view of the above, the effective content of Cr O has been found to fall within a range between 0.01 Weight percent and 0.30 weight percent for obtaining improved piezoelectric properties.

As already suggested above, the improvements made in the piezoelectric properties by the addition of Cr O and C0 0 clearly result from presence of chromium and cobalt ions. Chromium and cobalt ions may be introduced into the combination in various ways. Either chromium and cobalt oxides by themselves, or compounds thereof, which are easily decomposed at higher temperatures into the respective oxides such as shown in Tables 1 and 2, may be added to the powder of the raw materials of the basic composition during mixture thereof. For obtaining chromium ions, chromium sulfate [Cr (SO or the like may be substituted for chromium sesquioxide (Cr O Where 10:0.47, y=0.48, and z=0.05 and where x=0.42, For obtaining cobalt ions, cobalt carbonate (C000 or y=0.48, and z=0.10 and those obtained by adding therethe like may be used instead of cobalt sesquioxide to 0.10 weight percent of Cr O and 0.10 Weight percent (C 0 These chromium and cobalt compounds, other of C0 0 than Cr O and C0 0 should be used in their respective amounts which are equivalent to the desired amounts of results of Table 4 clearly shows that the substitution of Cr O and C0 0 as exemplified by the results Nos. 4 tin for a portion of the basic composition does not and 7 in Table 1 and the result No. 13 in Table 2. In harm the piezoelectric properties otherwise improved by this connection, it should be understood that chromium the coexistence of Cr O and Co O In other words, the

' sesquioxide (Cr O or cobalt sesquioxide (C0 0 as piezoelectric properties of the ceramic materials having these terms appear hereinafter, may also mean the tin substituted for a part of the basic compositions are respective chromium or cobalt compounds which is easily improved by the coexistence of Cr O and C0 0 as decomposed at higher temperatures into chromium sesquimuch as the ceramic materials having no tin substitution. oxide (Cr O or cobalt sesquioxide (C0 0 EXAMPLE 5 EXAMPLE 3 15 Results shown in Table 5 Results Shown inTable? Table 5 shows the results obtained by substituting Piezoelectric characteristics are shown in Table 3 for barium, strontium, and/or calcium for 5 atom percent typical ceramics obtained by selecting values of 0.50- of the lead in the composition No. 24 given in Table 4.

TABLE 5 Kr, No. Composition percent Qm 25 (Pbu.o5Bao.u5) (Zl'0.42Tl0,43sn0,10 03 plus 0.10 wt. percent ClzOa plus 0.10 wt. percent 58 1, 280

O2 3- 26 (Pgwg rms)(Zlo.42Tl0.45S110 10)O3 plus 0.10 wt. percent CrzOa plus 0.10 wt. percent 60 1, 250

O2 3- 27 (Pmrscaom) (Z1'o.42Tlu 4x8110100 plus 0.10 wt. percent CrzO; plus 0.10 wt. percent 56 1, 260

0.55 and 0.50-0.45 for x and y, respectively, in the for- As is seen from Table 5, the piezoelectric properties mula Pb(Zr Ti )0 and for those derived by adding are equally well improved by the coexistence of Cr O thereto 0.10 weight percent of Cr O and 0.10 weight and C0 0 for both compositions in which there has been percent of C0 0 a substitution of at least one alkaline earth metal selected TABLE 3 Kr, No. Composition percent Qm 15 Pb(Zlo.5uTlo,so)Oa 29 340 16-. Pb(ZI'0.50Tin.5u)O3 plus 0.10 Wt. percent 01'203 plus 0.10 Wt. percent 0020a. 55 1,330 17.- Pb(ZIo.53Tio.47) O3 41 300 18 Pb(Zr 5 Tlo.47)O3 plus 0.10 Wt. percent OrzO; plus 0.10 wt. percent 002 60 1, 270 19.. Pb(Zr0.55Ti0.45)0 39 320 20 Pb(Zro.5sTio.45)03 plus 0.10 Wt. percent 01-20 plus 0.10 Wt. percent 0020; 56 1,320

Table 3 clearly shows that changes of x and y in the from the group of any of the elements barium, strontium,

ceramic materials as noted, whose basic compositions are and calcium for a portion of the basic composition and given by the above formulae, do not materially alfect the for compositions having no such substitution. piezoelectric properties otherwise improved by the coexis- Examples 4 and 5 show that it is possible to provide tence of Cr O and C0 0 an excellent piezoelectric material by addition of both As a matter of fact, the compositions, improved by the Cr O and C0 0 with the basic compositions consisting addition of both Cr O and C0 0 have excellent propnot only of lead titanate-lead zirconate solid solution but erties for use in manufacturing the elements of ceramic also of lead titanate-lead zirconate-lead stannate solid electric wave filters and the transducers of mechanical solution and, still further, with compositions in which a 'fi1t s portion of the lead in these solid solutions is replaced by at least one alkaline earth metal.

EXAMPLE 4 As already observed, the piezoelectric ceramic composition improved as above noted can not be obtained by the addition of either Cr O or C0 0 alone, but only by the addition of both Cr O and C0 0 It is further noted that the piezoelectric properties referred to are Table 4 shows the piezoelectric properties of Kr and achieved through a polarization treatment performed at Qm for ceramics given by the formula Pb(Zr Ti Sn )O temperatures (about 50 C.-l50 C.) higher than room Results shown in Table 4 TABLE 4 Kr, No. Composition percent Qm Pb( 1o.47 l0.4sS 1o.o5)O3 40 280 Pb(ZI0.47TlU.4sSI10.05)O3 plus 0.10 wt. percent 01- 0 plus 0.10 wt. percent C0 0 58 1, 260 Pb(Zro 4zT1o.4aSI10,10)O3 41 300 Pb(ZIo.42Ti0.4aSn0,m)O plus 0.10 Wt. percent CD03 plus 0.10 Wt. percent 00 0 57 1, 320

Comparison of the result No. 5 of Table 1 with the temperature. The polarization treatment, if carried out at room temperature, reduces the value of Kr. Consequently, polarization at room temperature is consistent with the object of thisinvention.

EXAMPLE 6 Results shown in Table 6 In order that the resulting basic composition may be represented by the formula Pb (Zr Ti )O such composition was set up from a powder consisting of 50 mol percent of lead monoxide (PbO), 26 mol percent of zirconium dioxide (ZrO and 24 mol percent of titanium dioxide (TiO to which was supplied a compound of 0.02 weight percent of manganous oxide (MnO) as an additional constituent, and then a compound of cobalt sesquioxide (C0 0 of from 0.02 weight percent to 0.50 weight percent, as exemplified in Table 6, was added. These were mixed, respectively, in a ball mill. The mixed powder of the respective kinds was presintered at 900 C. for an hour, crushed, press-moulded into discs, and sintered at 1300 .C. for an hour. The resulting ceramic discs were provided with silver electrodes and piezoelectrically activated at 100 C. for an hour under an electric field of 50 kv./cm. After the discs had been allowed to stand for 24 hours, the electromechanical coupling factor Kr for the radial mode vibration and the mechanical quality factor Qm were measured to evaluate Referring to FIG. 3 of the drawing, the above-mentioned relation between the content of C0 0 and the piezoelectric properties Kr and Qm are plotted for the results Nos. 2 through 8 of Table 6. The curves quite clearly demonstrate that excellent piezoelectric materials are produced when the content of C0 0 falls between 0.02 weight percent and 0.50 weight percent.

When the content of C0 0 is less than 0.02 weight percent, the coexistence of MnO and C0 0 hardly improves the piezoelectric activities achieved by the presence of MnO alone. When the content of C0 0 exceeds 0.50 weight percent, there would be substantially no improvement in the activities over that which would otherwise be attained through the coexistence of MnO and C0 0 In view of the above, a range between 0.02 weight percent and 0.50 weight percent is selected for the effective range of the C0 0 content.

EXAMPLE 7 Results shown in Table 7 Table 7 shows the results obtained for a mixture of the basic composition of the same constituents as in Example 6 and an additional constituent of 0.10 weight percent of cobalt sesquioxide (C0 0 alone and also for various mixtures with additions of manganous oxide (MnO) of from 0.02 weight percent to 0.50 weight percent as noted in Table 7.

TABLE 7 No. Composition percent Qm 9 P'b(Zro,52Tln.4s)03 plus 0.10Wt. percent C020 56 350 10. Pb(Zr0.5zTlo.4s)O plus 0.02 wt. percent MnO plus 0.10 Wt. percent 00 0 59 360 11- Pb(Zro.52Tlo.4a)O3 plus 0.05 wt percent MnO plus 0.10 wt. percent 0020 64 400 12- b(Zr- 2Tio.4s)O3 plus 0.20 Wt percent MnO plus 0.10 wt. percent 0020: 68 450 l b(Zro 52Ti0 0 plus 0 Wt percent MnO 1 plus 0 10 wt percent 00 0 65 408 MnCOa is added as calculated on the basis of MnO.

the piezoelectric activities. Typical results obtained for the several cases are shown in Table 6.

Comparison of the result No. 1 of Example 6 with the result No. 9 of Table 7 shows that addition of 0.10 weight TABLE 6 Kr, N 0. Composition percent Qm Pb (ZluszTioAs) O3 42 250 260 59 360 66 470 Pb(Zru .52T1o,45)03 plus 0 20 wt percent NnO plus 0 10 wt percent C0203. 67 510 Pb(Z1'o.5zTlo.4t)Os plus 0.20 wt. percent MnO plus 0.20 wt. percent 00203 1 67 410 Pb(Z1'o.52Tlo.4s)Oa plus 0.20 wt. percent MnO plus 0.30 wt. percent C0203 64 370 8 Pb(Zro.52Tlo.4s)Oa plus 0.20 wt. percent MnO plus 0.50 wt. percent C0203 57 350 1 Cobalt carbonate (COCOa) is added as calculated on the basis of C0203.

The results Nos. 1 and 2 of Table 6 show that the addition of 0.20 weight percent of MnO alone to the basic composition provides a piezoelectric material of a fairly elevated Kr factor. The increase in the value of Kr and Qm due to the addition of MnO provides piezoelectric materials having a wider field of application and they serve as improved piezoelectric materials. A comparison of the results Nos. 1 and 2 of Table 6 with the results Nos. 3 through 8 of this table proves that addition of both MnO and from 0.02 weight percent to 0.50 weight percent of C0 0 to the basic composition remarkably raises both of the factors Kr and Qm.

As already observed, an increase in one of the factors Kr and Qm results in decrease in the other. However, the addition of both MnO and C0 0 to the basic composition as the additional constituents remarkably increases both Kr and Qm factors, thereby providing piezoelectric materials having raised Kr and Qm factors. Such materials are excellent for use in ceramic wave filters where large Kr factors are required and in transducers for mechanical filters.

Referring to FIG. 4 of the drawing, the piezoelectric properties Kr and Qm are plotted versus the content of MnO for the results of Table 7 and the result No. 5 of Table 6. This figure clearly shows that when the content of MnO falls between 0.02 weight percent and 0.50 weight percent, excellent piezoelectric materials are obtainable.

When the content of MnO is less. than 0.02 weight percent, the coexistence of MnO and C0 0 contributes but little to the improvement of the piezoelectric activities otherwise attained by the presence of C0 0 alone and responds little to improving the activities by the concurrent addition of MnO and C0 0 When the content of MnO exceeds 0.50 weight percent, the properties are so rigidly altered regardless of the presence of MnO that the coexistence of C 0 hardly improves the properties.

such composition 0.10 weight percent of MnO and 0.10 weight percent of C0 0 TABLE 8 Kr, No. Composition percent Qin 15 Pb(ZIo.5uTi0.s0) a 29 340 Pb(Zr ,5 Ti ,5o)O plus 0 10 wt percent MuO plus 0.10 Wt. percent Co Og 58 610 Pb(Z1"o,5 Tio,47 3 41 300 Pb(Zl'0 53Tlu 47)O3 plus 0 W percent MnO plus 0.10 wt. percent 0020;" 66 49 0 19 Pb(Z1'0 55Tiu,45) 03 39 320 20 Pb(Z1o.55Ti0,45)O plus 0.10 wt. percent M110 plus 0.10 Wt. percent C02Oa 62 590 In view of the above, a range between 0.02 weight per- 15 cent and 0.50 weight percent is selected for the effective range of the MnO' content.

As already suggested hereinabove, the improvements made in piezoelectric properties by the addition of both MnO and C0 0 clearly result from the presence of manganous and cobalt ions. Various ways may be employed to introduce manganous and cobalt ions into the compositions. As exemplified in Tables 6 and 7, the oxides themselves may be added, or, if desired, manganous or manganese and cobalt compounds may be employed provided they are decomposed into the respective oxides at elevated temperatures. It is thus possible to introduce manganous ions into the compositions by using, in place of manganous oxide (MnO), manganous carbonate (MnCO or any other manganous or manganese compositions, and, to introduce cobalt ions into the compositions, to utilize cobalt carbonate (CoCO or any other cobalt compound Table 8 clearly shows that change of x and y in the ceramic materials whose basic composition is given by the above-noted formulae does not degrade the piezo electric properties otherwise improved by coexistence of MnO and C0 0 Compositions improved by the addition of both M110 and C0 0 have excellent properties for use in manufacturing the elements of ceramic wave filters and the transducers of mechanical filters.

EXAMPLE 9 Results shown in Table 9 Table 9 shows the piezoelectric properties of ceramics given by the formula Pb(Zr Ti Sn )-O' where x=0.47, y-=0.48, and z=0.05 and where x=0.42, y=0.48, and z:0.l0 and those obtained by adding to each of the compositions 0.l0 weight percent of MnO and 0.10 weight percent of C0 0 as indicated in Table 9.

TABLE 9 No. Composition percent Qm 21 Pb(Z1o, 7Tl n 3Sno.05)O 40 280 22 Pb(Zro.41Tlu.4 SI10.05)Oa plus 0.10 wt. percent M110 plus 0.10 Wt. percent 01203. 62 470 23 Pb(Zrn.42Tiu.4eSn0.w)O,-i 41 300 24 Pb(Z1 4gT10.43SI10.10)O3 plus 0.10 Wt. percent MnO plus 0.10 Wt. percent 0020 61 520 instead of cobalt sesquioxide (C0 0 When manganous or manganese and cobalt compounds, other than MnO and C0 0 are utilized, they should be used in their respective equivalent amounts to effect the desired weight of MnO and C0 0 Use of such compounds is exemplified by the compositions No. 6 in Table 6 and No. 13 in Table 7. In this connection, it should be understood that, according to this invention, manganous oxide (MnO) and cobalt sesquioxide (C0 0 as used throughout this application, shall also mean and include such manganous or manganese and cobalt compounds which may be ther- EXAMPLE 10 Results shown in Table 10 Table 10 shows the results obtained by substituting barium, strontium, and/ or calcium for 5 atom percent of the lead in the composition No. 24 of Table 9.

TABLE 10 Kr, No C ompositiou percent Qm 25 (Pb0,% laa,6) (Z10 42Ti0.45$l'10.10)03 plus 0.10 Wt. percent MnO plus 0.10 wt. per- 520 C611 03 3. 26 (Pb ifir g (Zr Ti Snmo) 03 plus 0.10 wt. percent MnO plus 0.10 wt. per- 66 490 0011 02 3. 27 (Pb0 p5Cfl0.o5) (Zlu,4gTi0.48Sn0.l0)O3 plus 0.10 Wt. percent MnO plus 0.10 wt. per- 63 5, 000

cent C0203.

mally decomposed into manganous oxide (MnO) and cobalt sesquioxide (C0 0 respectively.

EXAMPLE 8 Results shown in Table 8 Piezoelectric characteristics are shown in Table 8 for typical ceramics obtained by selecting 0.50-0.55 and 0.50-0.45 for x and y, respectively, while maintaining 0.00 for z in the formula Pb(Zr Ti Sn )O by adding to lead zirconate solid solution but also of lead titanate-lead zirconate-lead stannate solid solution. Still further, excellent piezoelectric materials may be produced with such solid solution compositions in which a portion of the lead in these solid solutions is replaced by at least one alkaline earth metal.

While this invention has been set forth in certain particular compositions merely for illustration, it will be understood that the general principles of this invention may be applied to other and widely varied compositions without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. A piezoelectric ceramic composition having a basic composition represented by the following compositional formula (Pb A (Zr Ti Sn where A represents at least one member selected from a group consisting of calcium, strontium, and barium and u, v, x, y and z are given by characterized in that said ceramic composition contains a set of additional constituents consisting of a chromium compound equivalent in amount to a chromium sesquioxide of from 0.01 to 0.30 weight percent and a cobalt compound equivalent in amount to a cobalt sesquioxide of from 0.02 to 0.50 weight percent, each of the weight percentages being the percentage of the total weight of said ceramic composition.

2. A piezoelectric ceramic composition according to claim 1, wherein the set of said additional constituents consists of chromium sesquioxide of from 0.01 to 0.30 weight percentage and cobalt sesquioxide of from 0.02 to 0.50 weight percent, each of the weight percentage being the percentage of the total weight of said ceramic composition.

3. A piezoelectric ceramic composition having the following formula Pb (Zr Ti Sn 0 Where x=0.00-0.90, y=0.100.60, 2:0.00-065, and x+y+z=1.00,

characterized in that said ceramic composition contains a set of additional constituents consisting of chromium sesquioxide of from 0.01 to 0.30 weight percent and cobalt sesquioxide of from 0.02 to 0.50 weight percent, each of the weight percentages being the percentage of the total weight of said ceramic composition.

References Cited UNITED STATES PATENTS 2,928,163 3/1960 Berlincourt et al. 252-629 X 3,068,177 12/1962 Sugden 252-62.9

HELEN M. MCCARTHY, Primary Examiner J. COOPER, Assistant Examiner U.S. Cl. XR. 106--39 

